How to code autocompletion in python?

(I'm aware this isn't exactly what you're asking for, but) If you're happy with the auto-completion/suggestions appearing on TAB (as used in many shells), then you can quickly get up and running using the readline module.

Here's a quick example based on Doug Hellmann's PyMOTW writeup on readline.

import readline

class MyCompleter(object):  # Custom completer

    def __init__(self, options):
        self.options = sorted(options)

    def complete(self, text, state):
        if state == 0:  # on first trigger, build possible matches
            if text:  # cache matches (entries that start with entered text)
                self.matches = [s for s in self.options 
                                    if s and s.startswith(text)]
            else:  # no text entered, all matches possible
                self.matches = self.options[:]

        # return match indexed by state
        try: 
            return self.matches[state]
        except IndexError:
            return None

completer = MyCompleter(["hello", "hi", "how are you", "goodbye", "great"])
readline.set_completer(completer.complete)
readline.parse_and_bind('tab: complete')

input = raw_input("Input: ")
print "You entered", input

This results in the following behaviour (<TAB> representing a the tab key being pressed):

Input: <TAB><TAB>
goodbye      great        hello        hi           how are you

Input: h<TAB><TAB>
hello        hi           how are you

Input: ho<TAB>ow are you

In the last line (HOTAB entered), there is only one possible match and the whole sentence "how are you" is auto completed.

Check out the linked articles for more information on readline.

---

"And better yet would be if it would complete words not only from the beginning ... completion from arbitrary part of the string."

This can be achieved by simply modifying the match criteria in the completer function, ie. from:

self.matches = [s for s in self.options 
                   if s and s.startswith(text)]

to something like:

self.matches = [s for s in self.options 
                   if text in s]

This will give you the following behaviour:

Input: <TAB><TAB>
goodbye      great        hello        hi           how are you

Input: o<TAB><TAB>
goodbye      hello        how are you

---

Updates: using the history buffer (as mentioned in comments)

A simple way to create a pseudo-menu for scrolling/searching is to load the keywords into the history buffer. You will then be able to scroll through the entries using the up/down arrow keys as well as use Ctrl+R to perform a reverse-search.

To try this out, make the following changes:

keywords = ["hello", "hi", "how are you", "goodbye", "great"]
completer = MyCompleter(keywords)
readline.set_completer(completer.complete)
readline.parse_and_bind('tab: complete')
for kw in keywords:
    readline.add_history(kw)

input = raw_input("Input: ")
print "You entered", input

When you run the script, try typing Ctrl+r followed by a. That will return the first match that contains "a". Enter Ctrl+r again for the next match. To select an entry, press ENTER.

Also try using the UP/DOWN keys to scroll through the keywords.

To enable autocomplete in a Python shell, type this:

import rlcompleter, readline
readline.parse_and_bind('tab:complete')

(thanks to http://blog.e-shell.org/221)

I guess you will need to get a key pressed by the user.

You can achieve it (without pressing enter) with a method like this:

import termios, os, sys

def getkey():
    fd = sys.stdin.fileno()
    old = termios.tcgetattr(fd)
    new = termios.tcgetattr(fd)
    new[3] = new[3] & ~termios.ICANON & ~termios.ECHO
    new[6][termios.VMIN] = 1
    new[6][termios.VTIME] = 0
    termios.tcsetattr(fd, termios.TCSANOW, new)
    c = None
    try:
        c = os.read(fd, 1)
    finally:
        termios.tcsetattr(fd, termios.TCSAFLUSH, old)
    return c

Then, if this key is a tab key (for example, that's something you need to implement), then display all possibilities to user. If that's any other key, print it on stdout.

Oh, of course you will need to have getkey() looped in a while, as long as the user hits enter. You can also get a method like raw_input, that will get the whole word sign by sign, or display all the possibilities, when you hit a tab.

At least that's the item, you can start with. If you achieve any other problems, than write about them.

EDIT 1:

The get_word method can look like this:

def get_word():
    s = ""
    while True:
        a = getkey()
        if a == "\n":
            break
        elif a == "\t":
            print "all possibilities"
        else:
            s += a

    return s

word = get_word()
print word

The issue I'm occuring right now is the way to display a sign, you have just entered without any enteres and spaces, what both print a and print a, does.